Midterm 3 Study Guide

Midterm 3 will be Monday, November 25, 2019. The format will be the same as midterms 1 and 2.

This study guide has been updated for Fall 2019.

Long-answer Questions

One of these questions will be on the midterm.

  1. Compare and contrast osmoregulation and excretion in freshwater bony fish, marine bony fish, cartilaginous fish, lizards, and birds.
  2. Diagram and describe how the human kidney functions to make concentrated urine. (Hint: your answer should include Include both cortical and juxtamedullary nephrons. You don’t need to cover the hormonal regulation of kidney function.)
  3. Describe how hormonal systems and the kidney interact in humans to maintain homeostasis with respect to blood volume, pressure, and osmolarity.
  4. Belding's ground squirrels and large fish such as tuna or swordfish both face particular challenges with respect to thermoregulation. Describe these challenges and explain how thermoregulation works in these animals. Are they endotherms or ectotherms? Are they homeotherms or poikilotherms? (Hint: your answer should include both intrinsic factors related to the animal’s structure and behavior and extrinsic factors related to the environment. In the lecture PowerPoint I showed an image of circulation in a great white shark; the pattern is similar in bony fish such as tuna & swordfish.)

Important Concepts


  • Osmosis; osmoregulator; osmoconforming
  • Do fish drink water?
  • Isoosmotic, hyperosmotic, hypoosmotic
  • Isotonic, hypertonic, hypotonic
  • How substances cross membranes: simple diffusion, facilitated diffusion, active transport. Understand how this relates to membrane structure.
  • Paramecium contractile vacuole. What problem does it solve and how?
  • Nitrogenous waste: ammonia, uric acid, urea. Where does nitrogenous waste come from? Why do different animals have different forms? Why does it matter whether the nitrogenous waste is water-soluble?
  • Flatworm protonephridia. What problem do they solve and how?
  • Earthworm metanephridia. What problem do they solve and how?
  • Insect malphigian tubules. What problem do they solve and how? Why is it important that terrestrial insects produce uric acid?
  • Osmoregulation & excretion in fish: freshwater & marine bony fish; cartilaginous fish. Why are these groups of fish different from one another? Why are they different from terrestrial vertebrates? What organs are involved in osmoregulation and excretion for fish?
  • Vertebrate kidneys. What problem do they solve and how?
  • Filtration, reabsorption, secretion, excretion. Why do we do these things? Do all animals do them? Where do they happen in mammals?
  • Mammalian kidney; function of a nephron. Know the parts, and how Na+, Cl-, water, & urea move in each part.
  • Cortical and juxtamedullary nephrons
  • How is the osmotic gradient generated? Why is it important?
  • Blood vessels in kidney
  • Is the kidney a countercurrent exchanger?
  • Kidneys & overall osmotic strategies of birds, fish (freshwater marine, & sharks), and reptiles compared to mammals.
  • Adjusting urine osmolarity: roles of aquaporins, ADH (=vasopressin). In what situations would ADH level increase or decrease? How would this affect the kidney? How are the aquaporins added or removed? What else does ADH control, aside from the kidney?
  • RAAS: adjusting blood volume & pressure. What else does the RAAS system control, aside from the kidney? Why do we need both the ADH system and the RAAS system?
  • Vampire bats. Why is their situation extreme?
  • Factors affecting glomerular filtration rate.
  • Renal clearance rate. How is it related to filtration rate? How does clearance rate tell you if a substance is secreted or reabsorbed?
  • Reptiles: How does uric acid production help some animals to conserve water? How is the cloaca involved? Why do birds need to conserve water more than lizards?
  • Drinking seawater: compare human, seal, albatross. Where does the water go, and where does the salt go? Why does it matter if the urine is hyperosmotic? Hyperosmotic compared to what? What is the difference between the salt concentration and  the osmolarity of urine, and why do we need to consider both?
  • Salt glands: countercurrent multiplier.
  • Kangaroo rat strategies for dry conditions. Metabolic water vs. absorbed water. Why a low-protein diet is good for them.
  • Water budgets. Compare & contrast kangaroo rat, human, elephant seal pup. Why do the seals lose less water to evaporation?
  • The strange excretory strategy of the Chinese soft-shelled turtle
  • Osmoregulation Problems. Make sure you review the questions and answers; some of these ideas are likely to be on the test.

Energy & Thermoregulation

  • Why does thermoregulation matter?
  • Endotherms & ectotherms. Define & give examples. Why is it sometimes hard to say if an animal is an endotherm or an ectotherm?
  • Poikilotherms vs. homeotherms. Define & give examples.
  • Metabolic rates. How is it measured? What kinds of units could be used to express metabolic rates? Alligator vs. human: study the graph. Total energy use vs. mass-specific metabolic rate.
  • Energy budgets & thermoregulation. Why do the pie charts look different for the different animals? What determines the overall amount of energy used?
  • Importance of size
  • Thermoregulation in air vs. water. Why does performing gas exchange via gills in the water make it nearly impossible to be a homeotherm?
  • Compare & contrast: manatee, Steller’s sea cow, sea otter, marine iguana
  • Is thermogenesis necessary for thermoregulation?
  • Brown fat & non-shivering thermogenesis; compare to shivering thermogenesis.
  • Countercurrent heat exchange: Puffin feet, whale tongues, shark muscles, and insect bodies. Compare heat exchangers to other examples of countercurrent mechanisms.
  • Toucan bills: how can the toucan control how much heat it loses to the environment?
  • Sand gazelle: why is heterothermy influenced by the amount of water available? What does the carotid rete do?
  • Tuna & shark endothermy (or heterothermy). Why don’t they just keep their whole bodies warm? Why don’t they let their whole bodies be cold?
  • Swordfish eye warmers. Why? How?
  • Flying insects: Why they must be warm & how they do it. Endothermy & ectothermy in insects; heat flow from thorax to abdomen. Study the graph for preflight warmup in the hawk moth.
  • Japanese honeybees: heat as a weapon.
  • Torpor in ground squirrels and in hummingbirds. Why couldn’t these animals be complete endotherms or complete ectotherms?
  • Metabolic rate scales with size. What does this mean? Why is it true?
  • Large dinosaurs: why do researchers think that they weren't ectotherms?
  • Body temperature and lifespan. What does a survivorship curve say? What is the difference between the Baltimore longitudinal study of male humans and the study with transgenic mice? How do these relate to the calorie restriction study with monkeys?


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